Being able to control the phase, amplitude, and the polarization state of optical beams electrically has been a boon to engineers in many industries, especially in communications. Using electro-optic amplitude and phase modulators, it is possible to control the amplitude, phase, and polarization of optical beams by simply applying an electrical stimulus. In communications systems, these sorts of modulators are capable of impressing information directly upon an optical frequency carrier. Unlike lasers where the laser itself is modulated, external modulators dont cause a degrading effect on lasers line width and stability.
In measurement systems, it is possible for an amplitude modulator to be used as an actuator so that the intensity of a laser beam remains constant. Or, it can be used as an optical chopper to produce a pulsated stream from a CW laser beam. In many instances, phase modulators are commonly used in order to stabilize the various frequencies laser beams, or at least to mode-lock lasers.
In general, there are two basic types of modulators, types known as bulk and integrated-optic. In a bulk modulator, discrete parts of non-linear optical crystals are normally used on an optical table or lab bench. They characteristically feature very low insertion losses along with the capability to handle high power. Integrated-optic modulators, however, use waveguide technology so they can lower the required drive voltages. They also are wavelength specific, and, unlike bulk modulators, integrated-optic modulators are fiber pigtailed and extremely compact.
Light Measurement Integrating Spheres
Integrating spheres measure the total flux output of a myriad of different light sources, from LEDs, lasers, tungsten lamps, xenon arc lamps, and even fiber optics. The idea originated with Professor Richard Ulbricht, a renowned German engineer who worked on photometric investigations in the late 1890s. During his studies, he found that in a hollow sphere, wall lighting is directly proportional to the total luminous flux of the source of the light. He developed a measuring device that consisted of a ball-type photometer which he used as a calibration standard for lighting.
After the Frankfurt Electricity Exhibition in 1891, Germanys Royal Saxon State Railways decided they needed to build a three-phase electrical plant and called on Dr. Ulbricht to design and build it. Using his knowledge of the new integrating sphere concept, he designed and completed building the plant and it went into operation in 1897.
Ulbricht eventually published the details of his invention in 1900 and showed how many applications for which the device could be implemented. One of the most typical applications is to use the device as a test and calibration standard for different sensor characteristics.
Integrating Source Spheres
Integrating spheres are currently designed to calibrate and test cameras and numerous sensors like night vision systems, focal plane arrays, radiometers, ultra violet vision enhancement systems and optical detectors.
Custom Designed Versions
Custom designed integrating spheres are designed specifically to meet customer needs. They can be created in many different versions with varying sphere and port sizes; baffle sizes, styles and locations, stands and targets.
The practical implementation of the integrating sphere has become the most widely-recognized standard instrument used today in photometry and radiometry. It has many advantages for measuring light accurately and will continue to do so for the foreseeable future.